Stottite

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Stottite
Ludlockite-Leiteite-Stottite-170554.jpg
Pseudooctahedral, 2 mm large stottite crystal in germanite ore from the Tsumeb Mine, Namibia, accompanied by ludlockite and Leiteit (step size: 6.2 cm × 5.1 cm × 4.0 cm)
General and classification
chemical formula
  • Fe 2+ H 2 [GeO 4 ] • 2H 2 O
  • Fe [Ge (OH) 6 ]
  • Fe 2+ [Ge 4+ (OH) 6 ]
  • FeGe (OH) 6
  • Fe 2+ Ge 4+ (OH) 6
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.FC.15 ( 8th edition : IV / F.17)
03/06/07/01
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol tetragonal-dipyramidal; 4 / m
Space group P 4 2 / n (No. 86)Template: room group / 86
Lattice parameters a  = 7.594  Å ; c  = 7.488 Å
Formula units Z  = 4
Frequent crystal faces {111}, modified by {100}, {110}, {101}, {102} and {001}
Physical Properties
Mohs hardness 4.5
Density (g / cm 3 ) 3.596 (measured); 3.54 (calculated)
Cleavage good after {100} and {010}, indistinct after {001}
colour brown, green, orange, red; orange-brown in transmitted light, can be zoned with light olive-gray to almost colorless centers
Line color gray-white
transparency translucent to translucent
shine Resin to diamond gloss, greasy gloss on cleavage surfaces
Crystal optics
Refractive indices n ω  = 1.737-1.738
n ε  = 1.728
Birefringence δ = 0.01
Optical character uniaxial negative, abnormal biaxial
Axis angle 2V = small
Other properties
Chemical behavior soluble in 20% HCl

Stottite is a very rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the tetragonal crystal system with the chemical composition FeGe (OH) 6 and is therefore chemically an iron - germanium - hydroxide .

Stottite develops tetragonal-dipyramidal crystals up to 1 cm in size, which are pseudooctahedral and show the tetragonal dipyramid {111} as the supporting form.

Etymology and history

The Tsumeber miner Friedrich Gramatzki is considered the discoverer of stottite , who in October 1957 found a step with excellently formed, siderite-like crystals on the 30th level, which he could not classify, which is why he gave them to Hugo Strunz, who was then in Tsumeb for identification stayed. Corresponding investigations led to the determination of the presence of a new mineral, which a short time later, in 1959, was described by Hugo Strunz , Adolf Paul Gerhard Söhnge and Bruno H. Geier as stottite. The mineral was named after the geologist Charles E. Stott (1896–1978), who was general manager of the Tsumeb mine from 1953 to 1965.

Type material of the mineral is found at the Technical University of Berlin (holotype, collection no. 86/61, 86/62 at Pult 16, 89-1), at the École nationale supérieure des mines de Paris , France , and at Harvard University , Cambridge , Massachusetts (Catalog No. 111460).

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the stottite belonged to the class of "oxides and hydroxides" and there to the department of "hydroxides and oxidic hydrates (water-containing oxides with a layer structure)", where it was named after the " Stottit Group "with the system no. IV / F.17 and the other members Eyselit , Jeanbandyit , Mopungit and Tetrawickmanit .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies stottite in the newly defined division of "hydroxides (without V or U)". This is further subdivided according to the possible presence of OH and / or H 2 O as well as the crystal structure, so that the mineral is classified according to its composition and structure in the sub-section “Hydroxides with OH, without H 2 O; corner-linked octahedron "can be found, where together with jeanbandyite, mopungite and tetrawickmanite the" stottite group "with the system no. 4.FC.15 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns stottite to the class of "oxides and hydroxides" and there in the category of "hydroxides and hydroxides containing oxides". Here it is also together with jeanbandyite, mopungite and tetrawickmanite in the " Wickmanite group (tetragonal: P42 / n) " with the system no. 06.03.07 within the subsection “Hydroxides and hydroxides containing oxides with (OH) 3 or (OH) 6 groups”.

Crystal structure

Stottite crystallizes in the tetragonal crystal system in the space group P 4 2 / n (space group no. 86) with the lattice parameters a  = 7.594  Å and c  = 7.488 Å as well as four formula units per unit cell . Template: room group / 86

The crystal structure of stottite was originally described as follows: Fe and Ge form - each for itself - a slightly tetragonally deformed, face-centered cubic lattice: both lattices are placed one inside the other according to the NaCl type. Ge is surrounded by six (OH) in the form of a slightly distorted octahedron; Fe also forms a pseudo-octahedral coordination polyhedron with six (OH). The Ge (OH) 6 - octahedron and the Fe (OH) 6 octahedra are linked together by common edges. The surfaces of the morphologically dominant form {111} are structurally formed by slightly corrugated (OH) layers. The good cleavability according to the prism {110} and the base {00l} corresponds to the cubic cleavage of halite . This structure description was modified somewhat later. According to this, the stottite structure consists of a framework of Fe (OH) 6 and Ge (OH) 6 octahedra, which have common corners and which change in three dimensions. The lowering of the symmetry from ideally cubic to tetragonal is mainly due to the rigid rotation of the cation polyhedra . The average Fe-O distance is 2.159 Å, while the average Ge-O distance is 1.910 Å.

Chemism

Stottit the measured composition has (Fe 2+ 1.15 Mg 0.03 Mn 0.03 Ca 0.01 ) Σ = 1.22 Ge 4+ 0.95 (OH) 6 , which simplifies as FeGe (OH) 6 written and requires 45.38% GeO 2 , 31.17% FeO and 23.45% H 2 O. With 29% germanium, stottite has the highest germanium content of all known minerals.

Modifications and varieties

  • A pink variety of stottite containing zinc was first described in 1970 and designated as "Mineral A" or "zinc stottite", Zn 0.5 Fe 0.5 Ge (OH) 6 . At the original site of the Schneiderhöhnite in the area of ​​the 29th floor, in 1972, partly together with Schneiderhöhnite, partly sitting alone on adjacent rock, reddish translucent zinc stottite crystals with an edge length of up to 9 mm were observed. Around 1975 a pink-colored stottite variety containing zinc was found again - this time together with Schneiderhöhnit.
  • A manganese-containing stottite variety (“mineral B”, manganese analogue of stottite, MnGe (OH) 6 ), however, is only known in tiny formations. It was observed under an ore microscope in small flakes together with germanium- and zinc-containing mawsonite , Cu 6 Fe 2 SnS 8 . The name "manganese stottite" is used for it later.

Since 2007, "Mineral B", which is also regarded as the germanium-dominant analogue of tin-dominated wickmanite , has been referred to as "UM1970-16-OH: GeMn" with the formula (Mn, Fe) (Ge, Sn) (OH) 6 .

properties

Drawing of stottite crystals from the Tsumeb mine with different crystal dress

morphology

Stottite forms pseudooctahedral crystals up to 1 cm in size with the tetragonal dipyramid {111} as the supporting shape and clear stripes parallel to it [1 1 0]. The tetragonal prism {110} and the dipyramid {101} have been developed as a narrow truncated edge of this dipyramid, both of which together correspond to a slightly tetragonally deformed rhombic dodecahedron . The crystals are morphologically clearly characterized as tetragonal by the dipyramid {201}. The tetragonal prism {100} and the basic pinacoid {001} appear as small truncated corners. The combinations {111}, {100}, {001}, {110} and {011} or {111}, {100}, {001}, {011}, {021} and {110} observed, both of which have a pseudo-octahedral habit , as can be seen in the figure on the left.

physical and chemical properties

The crystals of the stottite are deep brown on the outside and light olive-gray to almost colorless on the inside, for which different levels of iron are responsible. The line color is given as gray-white. The surfaces of the translucent to transparent crystals have a resin-like to diamond-like sheen , while stottite has a greasy sheen on cleavage surfaces.

The mineral has good cleavage according to the tetragonal prism {100} and {010} and cleaves indistinctly according to the basic pinacoid {001}. With a Mohs hardness of 4.5, stottite is one of the medium-hard minerals that are somewhat easier to scratch with a pocket knife than the reference mineral apatite . The measured density of the mineral is 3.596 g / cm³, its calculated density is 3.54 g / cm³. Stottite dissolves in 20% hydrochloric acid .

Education and Locations

So far (as of 2016) the mineral could only be found at its type locality , the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia .

Stottit is a typical secondary mineral and formed in the second (lower) oxidation zone in dolomite stones seated hydrothermal polymetallic ore deposit Tsumeb. It emerged from the germanium-containing sulphides renierite and germanite from the Tsumeb ore body through the action of oxidizing seepage water warmed up to 35 ° C to 40 ° C at a depth of 1000 m.

On the first steps of the 30th level, which became known in 1957, stottite only sits in cavities in the tennantite ore. Further stages were found only a little later and then again in the 1980s. In 1972, zinc-rich stottite crystals were found on the 29th level together with Schneiderhöhnite and secondary chalcosine . Stottite was also found in the far west of the Tsumeb ore tube, in the "120 West" mine near the 29th level. Accompanying minerals here were brunogeierite , galena , tennantite (often with small renierite inclusions), smithsonite and, subordinately, cerussite . Some of the best crystals came from 950 m depth, in the area of ​​the 31st level, pillar E9. Other accompanying minerals are krieselite , ludlockite , Leiteit and siderite .

use

Regardless of the extremely high Ge content of 29%, stottite is not a germanium ore, but rather only of interest to mineral collectors due to its rarity.

See also

literature

  • Hugo Strunz, Gerhard Söhnge, Bruno H. Geier (1957): Stottite, a new germanium mineral, and its paragenesis in Tsumeb. In: New Yearbook Mineralogie Monatshefte , Volume 1957, pp. 85–96.
  • Stottit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 68 kB ).

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l Hugo Strunz, Gerhard Söhnge, Bruno H. Geier (1957): Stottite, a new germanium mineral, and its paragenesis in Tsumeb. In: New Yearbook Mineralogie, MONTHS , Volume 1957, pp. 85–96.
  2. ^ Hugo Strunz, M. Giglio (1961): The crystal structure of stottite Fe [Ge (OH) 6 ]. In: Acta Crystallographica , Volume 14, pp. 205-208.
  3. ↑ Mindat - Stottit
  4. ↑ a b c d Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  233 .
  5. ↑ a b c d e f g h i j k Stottit , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF, 68 kB ).
  6. ↑ a b c Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Grossenseifen 1999, p. 274-275 .
  7. ^ Type mineral catalog Germany - storage of the holotype stage Stottit
  8. ^ Charles R. Ross II, Lawrence R. Bernstein, Glenn A. Waychunas (1988): Crystal-structure refinement of stottite, FeGe (OH) 6 . In: American Mineralogist , Volume 73, pp. 657-661 ( PDF, 587 kB ).
  9. ↑ a b Bruno H. Geier, Joachim Ottemann (1970): New secondary Tin-Germanium and primary Tungsten- (Molybdenum-, Vanadium-) Germanium minerals from the Tsumeb ore-deposit. In: New Yearbook Mineralogie, Abhandlungen , Volume 114, pp. 89-107.
  10. ↑ Joachim Ottemann, Bernhard Nuber, Bruno H. Geier (1970): Schneiderhöhnit, a natural iron-arsenic oxide from the deep oxidation zone of Tsumeb. In: New Yearbook Mineralogie, MONTHS, Volume 1973, pp. 517-523.
  11. ↑ Georg Gebhard: Tsumeb . 1st edition. GG Publishing, Reichshof 1991, p. 190-191 .
  12. ↑ Wolfgang Bartelke (1970): The ore deposit of Tsumeb / South West Africa and its minerals. In: Der Aufschluss , Volume 27, pp. 393–439.
  13. ↑ William W. Pinch, Wendell E. Wilson (1977): Minerals: a descriptive list. In: Mineralogical Record , Volume 8 (Issue 3), pp. 17-36.
  14. ↑ Mindat - UM1970-16-OH: GeMn
  15. ↑ Mindat - Number of localities for stottite
  16. ↑ Find location list for stottite in the Mineralienatlas and Mindat
  17. ↑ a b Joachim Ottemann, Bernhard Nuber (1972): Brunogeierit, a germanium ferrite spinel from Tsumeb. In: New Yearbook Mineralogie, monthly books , volume 1972, pp. 263–267.
  18. ^ Ludi von Bezing, Rainer Bode, Steffen Jahn: Namibia. Minerals and sites (Edition Schloss Freudenstein) . 1st edition. Bode-Verlag, Haltern 2007, ISBN 978-3-925094-88-0 , p. 787 .
  19. ↑ Jochen Schlüter, Thorsten Geisler, Dieter Pohl, Thomas Stephan (2010): Krieselite, Al 2 GeO 4 (F, OH) 2 : A new mineral from the Tsumeb mine, Namibia, representing the Ge analogue of topaz. In: New Yearbook for Mineralogy, Abhandlungen , Volume 187 (Issue 1), pp. 33–40.